After years as the world’s biggest destination for recycled goods, China is getting sick of your scrap.

China imported about 2 million metric tons of aluminum, 10 million tons of plastic, and nearly 30 million tons of paper in 2015, according to industry figures. It’s been about 20 percent of US plastic bottles, a quarter of its paper and a third of other plastics, along with nearly 90 percent of what’s in Europe’s recycling bins. Much of that material helped supply China’s industrial boom or got turned back into consumer goods and shipped back to the West.

But after three decades of growth, the world’s second-largest economy is struggling to manage its own trash and pollution problems. And Beijing has complained that much of the recyclables it takes in are mixed with ordinary garbage or other wastes that can sicken the people who process it. So in July, the government announced it would ban imports of mixed plastic and paper, as well as many other scrap materials.

The ban, which takes effect in January, is aimed at cracking down on what the Chinese call “large amounts of dirty wastes or even hazardous wastes” that are coming in from abroad. But it’s left recyclers in the West scrambling to figure out what to do with all that paper and plastic.

“When China changes its mind on things, the ripple effect is global. It could definitely cause a lot of challenges for us here,” said Jennifer Turner, head of the China environment program at the Washington-based Woodrow Wilson International Center for Scholars. “They’ve become much more serious about environmental issues, and they are increasingly concerned about waste and wanting to recycle more.”

China’s transition to an industrial power has left the People’s Republic struggling with pollution on land, sea, and air. And as its own consumer economy booms, the country has to dispose of more waste of its own. So since 2012, Chinese authorities have been cracking down on imported recyclables they say are contaminated.

“This ban is a shot over the bow,” Turner said. “Foreign countries have got to give China exactly what it wants, how they want it, if we want to get rid of our stuff. But it’s also a shot over the bow for their own industries and their recycling industry.”

China is already a major destination for electronic waste, a lucrative trade that also can be hazardous to the environment and the people who recycle it. The recycling sector is largely unregulated, with mom-and-pop operators competing alongside sophisticated, high-tech operations.

But ahead of January’s ban, the government has been cracking down on importers and even shutting down some companies that take in more than permitted, said Anne Germain, vice president for technical and regulatory affairs at the National Waste and Recycling Association in Washington.

In addition to the ban on plastics and mixed paper, other materials like newsprint and cardboard boxes will be subject to a tight standard of cleanliness. Extraneous waste can’t make up more than half of one percent of the weight of the shipment — a standard Germain said is all but impossible for US recyclers to meet.

“We consider ourselves to be environmentalists,” said Germain, whose organization represents American recycling companies. “We support all their efforts to improve their environment, and we ultimately think that will be a good thing.”

US recyclers have been trying to convince China to loosen the new rules. So far, they’ve succeeded in getting the contamination standard raised from 0.3 percent to 0.5 and pushed that rule’s implementation back until March, Germain said. But the industry isn’t sure yet where wastes that would otherwise be bound for Chinese ports will end up.

“Nobody’s going to be able to instantly replace China. It’s just not that easy,” she said. California alone ships more than 80 percent of its mixed paper there, and other countries like India are considering similar restrictions. US companies have talked about opening new recycling operations here, “But they’re not expected to be open in a year — two years if you’re lucky.”

Some recyclables are already piling up in American facilities, and Germain’s organization is urging them to keep their material “as clean as possible” in hopes of finding buyers. And American consumers should avoid what the industry calls “wishful recycling” — tossing in things that aren’t recyclable, like soiled food containers or bottle caps.

“This is part of what contributed to the contamination rate that China finds so problematic, and frankly, there are lots of issues we have at recycling facilities,” she said. People should check with their local recycling program to find out what they do and don’t take, “not just throw it in the recycle bin and hope we fix it at the plant.”

“The things you should focus on recycling are the core recyclables — newspapers, office paper, cardboard boxes, and containers,” she said. If you’re in doubt about it and you’re not going to spend the time finding out, throw it out.”